Mr Bridges denies any wrongdoing and says that donation and another for $14,000 were mistakenly attributed to his personal electoral return, rather than the National Party itself.

Aaron Bhatnagar has revealed he is the National Party donor behind the $10,000 'Cathedral Club' donation.
Photo credit: Facebook

Mr Bhatnagar is a well-known National supporter and he is brushing off the controversy.

"These days, it's easier for me to donate to parties, causes and charities than it is to participate on committees and help in campaigns as I once did.

"I'd rather be following my passions of watching my children play football, collecting NZ art, and getting involved in some great NZ tech companies.

"So I'm happy to be noted as giving $10,000 to the National Party in 2017. In addition, I have supported candidates in National with lesser sized donations in the past."

Exactly why the name Cathedral Club was used instead of Mr Bhatnagar's is unknown - if the $10,000 was a donation to National rather than Mr Bridges, he didn't have to be identified as the donor anyway, as it falls within the $15,000 limit for anonymous donations.

"Cathedral Club was an informal pay-your-own-way dinner club that started in 2001, comprised of a small group of Young Nats and old friends from university days," Mr Bhatnagar said.

He was a regular dinner attendee and one of the organisers.

"The last dinner was probably around 2008."

Former National Party staff member and right wing political commentator David Farrar remembers attending a dinner the Cathedral Club hosted 12 years ago.

"What it was, was a group of centre right young people in Auckland... who would go out for dinner at the Auckland Club, in the Cathedral Room of the Auckland Club, and they'd have an interesting guest speaker," Mr Farrar told Newshub.

Those guests came from across the political divide, with Winston Peters and Dr Michael Bassett among those addressing the club.

Mr Ross said on Tuesday, at an explosive press conference held at the Beehive while the National Party voted to expel him, that he has a recording that proves his allegations. He filed a complaint with police on Wednesday.

Mr Farrar calls the alleged corruption a "very serious accusation".

"If you take it literally at what Jami-Lee has alleged, he's actually saying Simon Bridges, a former Crown Prosecutor, is a criminal and should be in jail because the maximum sentence for these is actually two years' imprisonment. So it's an incredibly serious thing."

He says any criminal case will come down to the details of that tape, "but also the details of what actually happened, was there money paid, who was it from".

Mr Farrar, who is also a political pollster, thinks the ongoing fallout will hurt National in the polls.

"It will do damage but it might not last for longer than this is in the news."

He says National will struggle for coverage on other issues they care about while this is the media focus.